It is known to control electrical motor operation by a microcomputer or other controller via an interface which interprets control commands and suitably applies on or off signals to switching circuitry which drives the motor. A useful motor driver capable of forward and reverse operation is an H-bridge which has two arms connected from opposite sides of the motor to the power source and two more arms connected from opposite sides of the motor to ground. Each arm contains a switch such as a power MOSFET or other semiconductor switch so that by selective switch control the motor can be driven in either direction by current flowing from the power source and through the motor to ground.
The control of motor current is carried out by dIrect pulse width modulation in response to pulsed controller signals so that the average motor current is that desired by the controller r, or by a current value signal from the controller which is compared with a current feedback signal from the driver circuit to regulate the drivers on and off. Throughout all these control operations it is necessary to manage the switching in a manner which avoids damage to the semiconductors and which also avoids damage to the motor. That is, in the case of improper controller signals or faulty motor operation the motor current should be turned off or kept off. Then any switch currents which are not predictable and within safe limits are prevented or immediately terminated. To assure that requested currents and other commands are correct it is important to have frequent updates from the controller. The absence of such frequent updates suggests that the controller is faulty.